1. Field of Invention
This invention relates to the nondestructive measurement of the moisture content of individual single grain kernels, seeds, nuts, or fruits.
2. Description of the Prior Art
The moisture in cereal grains, seeds, nuts, and fruits is presently measured in bulk samples, and most of the available grain moisture meters are suitable for bulk samples only. The bulk values thus measured do not always represent the moisture content of every kernel in the bulk sample and do not provide any information on the range of moisture contents of the individual objects or kernels within the sample. Kandala ]M. S. Thesis, The University of Georgia, Athens, Ga. (1987)] reported earlier that single kernel moisture content in corn (maize), Zea mays L., can vary as much as .+-.0.8% on a wet basis (w.b.) from the bulk value as obtained by air-oven drying tests on single kernels and bulk samples from well-conditioned corn samples. Larger variations are expected in unconditioned samples. Further, the blending of grain with high levels of moisture with grain of permissible levels for safe storage can be conducive to the growth of microorganisms and may lead to spoilage. Concern has developed that spoilage of grain in transit or storage may be related to the practice of blending (mixing) of grain lots of different moisture levels.
Measurements of impedance on individual corn kernels with capacitive sensors at radio frequencies have been used to determine single kernel moisture content. Kandala et al. ]International Agrophysics 4(1-2): 3-12 (1988); Trans. ASAE 31(6): 1890-1895 (1988); Trans. ASAE 30(3): 793-797 (1987)] nondestructively measured the capacitance and dissipation factor of a small parallel plate capacitor with single kernels of corn between and in contact with the plates to determine kernel moisture content.
Electrical resistance of single kernels passing between crushing roller electrodes is also used for single kernel moisture determination.
Bussey ]Proc. IEEE 55(6): 1046-1053 (June 1967)] discussed the use of microwave resonant cavity techniques to measure the microwave and dielectric properties of materials by measuring the shift in the resonant frequency and the change in the Q-factor of the cavity when the sample is inserted into the cavity. However, Bussey did not disclose the measurement of the moisture contents of articles of variable or nonuniform shape.
Kraszewski et al. [IEEE Transactions on Instrumentation and Measurement 38(1): 79-84 (February 1989)] disclose a nondestructive process for the determination of moisture content in single soybean seeds using a microwave resonator. A seed is placed in a microwave resonant cavity and the resonant frequency shift and change in Q factor are measured. However, while this process allows the measurement of moisture content of articles of nearly uniform spherical shape, it does not provide for the accurate measurement of nonuniform, irregularly shaped objects.